Means for improving the yield from betatron x-ray generators



Feb. 16, 1954 G. D. ADAMS ET AL 2,669,652.

MEANS FOR IMPROVING THE YIELD FROM BETATRON X-RAY GENERATORS Filed Dec. 15, 1948 FIG.I

FIG. 4

INVENTOR. Gqil D. Adams Donald W. Kers'r BY W UNITED STATES PATENT OFFICE MEANS FOR IMPROVING THE YIELD FROM BETATRON X-RAY GENERATORS Gail D. Adams and Donald W. Kerst, Urbana, Iil., assignors to the United States of America as represented by the Secretary of the Navy Application December 15, 1948, Serial No. 65,493

7 Claims.

This invention relates to the magnetic induction accelerator and more particularly to coils for correcting the magnetic field of the ma netic induction accelerator.

In the practical operation of the magnetic induction accelerator it has heretofore been found that local field variations occur as a result of errors in manufacture or result from constructional accidents causing a departure from the shown a closed glass vessel 18 defining within its interior the continuous annular acceleration chamber 28. The magnet assembly comprises a pair of juxtaposed circular pole pieces 24 and 25 respectively supported on conically tapered parts 23 and 25. The tapered parts are in turn mounted on main poles 2B and 22. A more complete description is given in United States Patent 2,297,- 305 to Kerst. As disclosed in this patent, the

desired optimum conditions, especially with re- 10 acceleration chamber includes an electron inspect to the similar phasing of the alternating jection comprising a thermionic cathode and field at the inner and outer portions, respectively, other electrode structure capable of injecting thereof. electrons tangentially into the electron orbit of It is therefore an object of our invention to the acceleration chamber whenever the magcorrect the magnetic field of a magnetic inducnetic field of the betatron is at a minimum. Also, tion accelerator. means including saturable means are provided Another object of our invention is to correct to disturb the magnetic field whenever the magphase variations in the magnetic field emanating netic field approaches a maximum so as to shift from the pole pieces of a magnetic induction acor eject the electrons, while near maximum veloccelerator. ity, from the electron orbit whereby the ejected In the attainment of the foregoing objects it electrons impinge upon a target located within is a feature of our invention to provide an atthe acceleration chamber. tachable coil capable of inducing magnetomotive The wire wound support 6 of Fig. 1 is here forces in the pole pieces of a magnetic induction shown between the glass vessel I8 and the pole accelerator. piece 25. A view of this support 6 in said position The phases of this invention which I desire is shown in Fig. 3 by a cross-section taken on to protect herein are particularly pointed out line 55. Here the po piece 6 and the tapered in the appended claims. The invention itself pole 25 are shown as defining the radial distances together with further objects and advantages I2 and I4 previously mentioned. Asuitable varithereof can best be understood by reference to able resistor 32 is shown in series with the coil the following description of the accompanying 8 to provide a means of varying the strength of drawings of Which 1 s a schematic viewsu the coils field. The variable resistance acts ably embodying the invention; Fig. 2 is the mageffectively to vary the total impedance of the net and acceleration chamber assembly of a circuit thereby to control the current flow theremagnetic induction accelerator; Fig. 3 is a, cross- 35 through from an electrical power source. Hence, section taken on a line 5-5 of Fig. 2 and Fig. 4 the amount of current fiow through the coils is a cross-section taken on a line 'i! of Fig. 2. will determine the strength of the resultant field Referring particularly to Fig. 1 there is shown produced by the coil. The corrector coil opera corrector coil comprising a trapezoidal shaped ates to cancel the phase variations of the magsupport 6. A number of turns of Wire 8 is wound 40 netic field caused by residual magnetic fields due around the P r p ery of this support alter e to hard spots in the pole faces, eddy currents and above and below it between the slots l0 out thereother similar causes by producing an opposing in or the P p Of transposition The S p magnetic field to such disturbing erratic mag- Of t S pp is determined by the a e of netic fields. By locating the corrector coil upon divergence 16 of the trapezoid and, as will be ext main poles in an optimum position, such as plained more fully later, the radial distances l2 hown in Fig. 3, and by providing a magnetic and I4. field of sufficient strength to overcome the erratic The magnet and acceleration chamber assemmagnetic fields, the magnetic field of the pole bly of a conventional magnetic induction accelpieces will be phase corrected. Originally, finderator is depicted in Fig. 2 in which there is n the p m position of a coil was large y a trial and error method, however, recently means were developed to make an accurate survey of the magnetic field and hence to establish quantitatively to what extent such a coil would be needed and where it should be placed. The action of this coil is to make the magnetic field in all azimuths of the pole pieces have the same phase. This means that the magnetic field at a given radius from the center of the pole and at any instant is the same for any azimuth. The efiect is important only for the short time in the neighborhood of and .following the injection of electrons, which is at small or minimum magnetic field intensity.

A coil was designed for a particular magnetic r chanical protection and to a lesser exent electrical insulation. This coil, operating on the magnetic induction accelerator for which it was designed, gave ahundred percent increase in X-ray output.

In Fig. 2 there isalsor-shown :arsecond type of coil -39 shown moreparticularly in -Fig.'.4:inmhich the coil .30 .is shown as wound around the pole piece 23 and having a resistor Miniseries there-, with to vary the-coilfs magnetic field. Thistype of coil is to be used :in caseone pole as a whole is out of phase with its mate.

While the invention is herein described by reference to particular embodiments thereof, it will be understood that numerous modifications may be made without actually departingt-from the true spiritand scope of the invention.

.Having thus described-our inventiomwhat we claim is:

1. In combination with a magnetic .induction accelerator containing an electromagnet :having pole pieces out of phase with oneanother means for correcting said phase .difierences, said means including an electrically energizable coil .having its magnetic axis .parallel toand displaced from the magnetic axis of said electromagnet adjustably positioned .adjacent -.one :of .said pole pieces soas to induce a magnetomotive force .in said one of said pole pieces, saidmagnetomotive force being of such-magnitude and in such.-.a.direction as .to compensate .for .said ,phase differ ences thereby causing the pole. pieces .to.be in phase with-one another.

2. .In .a magnetic induction .acceleratorhaving an evacuated acceleration .channel encircling pole pieces of an alternating current-.excitedfild magnet, a'thin support member of insulating material disposed between one of said pole pieces or said magnet and said channel andpositioned adjacent one side of said onepolepiece and anemcorrecting coil supported by said support member, said coil being energized continuously iindirection and amount to substantially canclfhe residual flux Jtherethrough from said magnet 'whenthe fiux from -the'remainder of themagnet is at a-minimum'in each cycle oisaid 'energization.

3. In a magnetic induction accelerator employing afield magnet periodically 'energ'izedin opposite "directions and having an accelerating channel surrounding pole pieces of 'themagnet, a fiat field correcting coil having sides arranged substantially radially from the ccnter'br asaid pole piece and arcuate members completing said coil, the arcuate members having a common are center, means supporting the coil in adjustable location between said channel and magnet, and means controlling the current in the coil, whereby direct current energization thereof is adjustable to efiect a maximum degree of phase equalization in the flux from the magnet.

4. In a magnetic induction electron accelerator having a magnet energized by alternating current and an acceleration channel encircling pole pieces of the magnet, a thin coil support adjustable between the channel. and said pole pieces of said magnet, a correcting coil mounted on said support having a resistance in series therewith and terminals for energization thereof, and'means for adjusting the direct current resistancebetween said terminals, whereby a phase change .-in theportion of the magnetic field induced :by-said v:magnet and passing through the correcting coil as v:said magnet is alternatingly energized is .efiected in proportion to direct current energization of said correcting coil, the amount of said phase change being controllable by said adjusting means.

5. .In .a .magnetic induction accelerator having a fieldmagnet with proximately disposed poles and energized with alternating current, said accelerator having an annular accelerating channel between said poles, .ajdevice for testing the uniformity of ,phase .of .the magnetic .field produced .by said current comprising a .thin trapezoidal support insertable betweensaid channel and eitherof said poles and movable circumferentiallyiand inwardly and outwardly with respect .tQ-ithe pole center, a .coil disposed about the periphery ofsaid support and-secured .thereto,.and means for varying the magnitude of current in said coil in response .to direct current energize.- tion fthereci, whereby 'the coil .is .adjustablein position and magnitude of phase-correctinge'ffeet on the field .of said magnet as .thefield approaches zero on each cycle.

'6. In an alternating current magnetic induction accelerator containing electromagnetic pole pieces and an electronchannel disposed about a space'between said pole pieces, said channel having means for inserting a stream of electrons tangentially within said channel when saidifield is at a minimum and means for disturbingthe field through .the pole pieces when the Jfield (ap- .proac'hes maximum .in order to ejectsald .electrons at near maximum velocity, additional correotor coil means energizeiiby .direct .currentand lyingfbetweensaidpole pieces and the sidesof saidlchannel. for disturbing the normal ,phase relationship .cr .themagnetic fieldiinduced by. said pole. pieces, .and .means variably controlling .the amount ofsaid disturbance of phase. relationship, whereby said relationship .may 'be made .to equalize .to ithereby increase the percentage of electronsinserted in said channel at .said minimum 'fiel'cl.

37.."In .an alternating. .current .magnetic induc- Ztionaccelerator having proximately disposedpole pieces and an electron chann'el .therearoundand equipped. withmeansinj ecting electrons into said channel at minimum .field conditions .and..other meansupsetting thenormal field distribution at approximatelycnaximum .fie'ld conditions thereby .to eiectsaid electronsatihigh velocity, additional means comprising a field producing correctoncoil between said channel and said polepieces at a set'distance from the centers of the pole pieces, saidadditional-means=producinga field inphase quadrature to the field of said accelerator induced by said alternating current for altering the phase of a portion thereof, and means for varying the strength of field from said additional means, whereby the resultant phase change in said field portion increases the acceptance of electrons accelerated in said channel and the ejection of said electrons at high velocity.

GAIL D. ADAMS. DONALD W. KERST.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Wilson July 10, 1928 Penney Mar. 12, 1940 DEntremont May 26, 1942 Kerst Sept. 29, 1942 Baldwin Oct. 12, 1943 Jenkins Dec. 17, 1946 Stuart, Jr June 3, 1947 Westendorp Dec. 13, 1949 Wideroe Oct. 23, 1951 Wideroe Feb. 19, 1952 

